Samantha Stosur has revealed her disappointment at having to pull out of Thursday's BNP Paribas Open quarter-final against Angelique Kerber through injury.

The Australian seventh seed picked up the problem in the final game of her fourth-round victory against Mona Barthel on Wednesday.

"I don't know if you can get any more unlucky than that," Stosur said in a statement. "I think we only played another four points in that match. I felt something go in my calf and it was hurting a fair bit.

"Yesterday I took the day off practice and only did treatment, probably iced it about 10 times. This morning I thought I would give it a shot and tried to go out and warm up.

"After about five minutes, I knew that there was no chance I could play unfortunately. I think this is only the second time I've ever pulled out of a match in my career."

Kerber will face either Victoria Azarenka or Caroline Wozniacki for a place in the final.